CVE-2021-39164: Improper authorisation of /members discloses room membership to non-members
First published: Tue Aug 31 2021(Updated: )
### Impact Unauthorised users can access the membership (list of members, with their display names) of a room if they know the ID of the room. The vulnerability is limited to rooms with `shared` history visibility. Furthermore, the unauthorised user must be using an account on a vulnerable homeserver that is in the room. ### Patches Server administrators should upgrade to 1.41.1 or later. ### Workarounds Administrators of servers that use a reverse proxy could, with potentially unacceptable loss of functionality, block the following endpoints: * `/_matrix/client/r0/rooms/{room_id}/members` with `at` query parameter * `/_matrix/client/unstable/rooms/{room_id}/members` with `at` query parameter ### References n/a ### For more information If you have any questions or comments about this advisory, e-mail us at security@matrix.org.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Matrix Synapse | <1.41.1 | |
| Fedoraproject Fedora | =34 | |
| Fedoraproject Fedora | =35 | |
| pip/matrix-synapse | <1.41.1 | 1.41.1 |
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Reference Links
- https://github.com/matrix-org/synapse/commit/cb35df940a
- https://github.com/matrix-org/synapse/releases/tag/v1.41.1
- https://github.com/matrix-org/synapse/security/advisories/GHSA-3x4c-pq33-4w3q
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF/
- https://nvd.nist.gov/vuln/detail/CVE-2021-39164
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-425.yaml
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/2VHDEPCZ22GJFMZCWA2XZAGPOEV72POF
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PXT7ID7DNBRN2TVTETU3SYQHJKEG6PXN
- https://github.com/advisories/GHSA-3x4c-pq33-4w3q (Advisory)
Frequently Asked Questions
What is CVE-2021-39164?
CVE-2021-39164 is a vulnerability in Matrix Synapse versions 1.41.0 and prior that allows unauthorized users to access the membership (list of members) of a room if they know the room ID and the room has shared history enabled.
What is the severity of CVE-2021-39164?
The severity of CVE-2021-39164 is low, with a CVSS severity score of 3.1.
How can unauthorized users access the membership of a vulnerable room in Matrix Synapse?
Unauthorized users can access the membership of a vulnerable room in Matrix Synapse if they know the room ID and the room has shared history enabled.
Which versions of Matrix Synapse are affected by CVE-2021-39164?
Matrix Synapse versions 1.41.0 and prior are affected by CVE-2021-39164.
How can I fix CVE-2021-39164 in Matrix Synapse?
To fix CVE-2021-39164, upgrade to version 1.41.1 or later of Matrix Synapse.
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